The invention relates to a process for the preparation of polycarbonates and more particularly the interfacial polycondensation process.
For the preparation of polycarbonates by the so-called interfacial process, dihydroxydiarylalkanes in the form of their alkali salts are reacted with phosgene in heterogeneous phase in the presence of inorganic bases such as sodium hydroxide solution and an organic solvent in which the product polycarbonate is readily soluble. During the reaction, the aqueous phase is distributed in the organic phase, and after the reaction the organic polycarbonate-containing phase is separated from the aqueous phase and washed several times with an aqueous liquid, during which electrolytes, residual monomers and catalyst inter alia are removed. The washing liquid is then separated off as far as possible. Finally, the polycarbonate is freed of the organic solvent and converted into a form which may readily be processed further, for example granular form.
This known interfacial process is described by way of example and in detail in the following publications:
Schnell, xe2x80x9cChemistry and Physics of Polycarbonatesxe2x80x9d, Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney 1964, p. 33 ff;
D. C. Prevorsek, B. T. Debona and Y. Kesten, Corporate Research Center, Allied Chemical Corporation, Morristown, N.J. 07960: xe2x80x9cSynthesis of Poly(ester Carbonate) Copolymersxe2x80x9d in Journal of Polymer Science, Polymer Chemistry Edition, Vol. 18, (1980), p. 75 ff;
D. Freitag, U. Grigo, P. R. Mxc3xcller, N. Nouvertne, BAYER AG, xe2x80x9cPolycarbonatesxe2x80x9d in Encyclopedia of Polymer Science and Engineering, Volume 11, Second Edition, 1988, p. 651 ff; and finally
Dres. U. Grigo, K. Kircher and P. R. Mxc3xcller, xe2x80x9cPolycarbonatexe2x80x9d in Becker/Braun, Kunststoff-Handbuch, Volume 3/1, Polycarbonate, Polyacetale, Polyester, Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, p. 118 ff and 138 ff.
These publications relate to corresponding syntheses of polycarbonate according to the so-called xe2x80x9cinterfacial processxe2x80x9d, which takes place in a two-phase reaction mixture consisting of inorganic phase (water, alkali) and an organic phase (organic solvents, insoluble in water, mostly chlorinated hydrocarbons such as dichloromethane and/or chlorobenzene).
The product of that synthesis is an organic phase (synthesis solution), which contains the polycarbonate in dissolved form, and an inorganic aqueous-alkaline phase, which contains the salts formed in the synthesis, such as NaCl, sodium hydrogen carbonate, soda, additionally residues of the phenolates, bisphenolates and sodium hydroxide used, as well as catalysts and secondary products thereof, as well as water-soluble compounds originating as impurities from the starting materials or formed as by-product. If a different basic compound is used instead of NaOH, the aqueous alkaline phase contains the corresponding analogous salts or secondary products.
The aim of the working-up which follows is to separate off the inorganic aqueous phase as completely as possible and to remove the remaining, especially alkaline residues of the inorganic compounds, which are contained in the soluble and dispersed water content of the separated organic phase, as completely as possible from the organic phase. This is achieved by washing operations, which are optionally combined with acidification steps. If possible, these purification operations are carried out before concentration of the organic phase, if thermal methods are used for the purpose of concentration.
Purification of the synthesis solution is achieved by washing that organic solution with water one or more times. In general, this is effected by means of one or more acidification operations and washing with water, mostly in several steps.
The acidification includes either the entire alkali potential of the synthesis or preferably, after separation of the phases in the alkaline pH range, only the neutralization of residual constituents of the aqueous phase dissolved or, in admixture with residues of the aqueous phase, dispersed in the organic phase. There are used for such acidification operations aqueous mineral acids, especially hydrochloric acid and phosphoric acid, but also aqueous solutions of organic acids.
This washing and acidification is likewise the subject-matter of many patents and publications.
For example, EP-A 0 023 570 describes a process for working up the alkaline synthesis solution using separators that produce shear energy, optionally with the use of dispersing agents.
According to the invention, polycarbonates are to be understood as being those based on suitable diphenols, for example hydroquinone, resorcinol, dihydroxydiphenyl, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl) sulfides, bis-(hydroxyphenyl) ethers, bis-(hydroxyphenyl) ketones, bis-(hydroxyphenyl)-sulfones, bis-(hydroxyphenyl) sulfoxides, xcex1,xcex1xe2x80x2-bis-(hydroxyphenyl)-diisopropylbenzenes, and also compounds thereof alkylated at the nucleus and halogenated at the nucleus.
Preferred diphenols are hydroquinone, resorcinol, 4,4xe2x80x2-dihydroxydiphenyl, 2,2-bis-(4-hydroxyphenyl)-1-phenyl-propane, 1,1-bis-(4-hydroxyphenyl)-phenyl-ethane, 2,2-bis-(4-hydroxyphenyl)propane, 2,4-bis-(4-hydroxyphenyl)-2-methylbutane, 1,1xe2x80x2-bis-(4-hydroxyphenyl)-m- or -p-diisopropylbenzene, 2,2-bis-(3-methyl-4-hydroxy-phenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-methane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone, 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane, 1,1xe2x80x2-bis-(3,5-dimethyl-4-hydroxyphenyl)-m- or -p-diisopropylbenzene and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
Particularly preferred diphenols are resorcinol, 4,4xe2x80x2-dihydroxydiphenyl, 1,1-bis-(4-hydroxyphenyl)-phenyl-ethane, 2,2-bis-(4-hydroxyphenyl)-propane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, 1,1xe2x80x2-bis-(3,5-dimethyl-4-hydroxyphenyl)-m- or -p-diisopropylbenzene, 1,1-bis-(4-hydroxyphenyl)-cyclohexane and 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
These and other suitable diphenols are described, for example, in U.S. Pat. Nos. 3,028,635, 2,999,835, 3,148,172, 2,991,273, 3,271,367, 4,982,014 and 2,999,846, in DE-A 1 570 703, 2 063 050, 2 036,052, 2 211 956 and 3 832 396, French Patent Specification 1 561 518, in the monograph xe2x80x9cH. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964xe2x80x9d, p. 77 ff and in JP-A 62039/1986, 62040/1986 and 105550/1986.
In the case of homopolycarbonates, only one diphenol is used, and in the case of copolycarbonates a plurality of diphenols is used, it being possible, of course, for the bisphenols used, like all the other chemicals and auxiliary substances added to the synthesis, to be contaminated with the impurities from their own synthesis, although it is desirable to use raw materials that are as clean as possible.
As carbonate precursor there are used halogen derivatives of carbonic acid, such as are described in the cited literature, especially phosgene.
Catalysts include ammonium and/or phosphonium compounds or tertiary amines such as are described in the literature, especially N-ethylpiperidine, N-methylpiperidine, triethylamine and tributylamine, or mixtures thereof, it being possible for such catalysts to be added in a single metered amount or alternatively the metering in of several amounts at time intervals (batch process) or in space (continuous process).
There may be used as the alkaline components any alkali and alkaline earth hydroxides that are soluble or dispersible in water, but preferably sodium hydroxide, potassium hydroxide, magnesium hydroxide and/or calcium hydroxide (suspension of calcium oxide in water) or mixtures thereof.
The solids content of the polymer solution to be washed may vary according to the molecular weight of the polymer of 0.5 wt. % to 30 wt. % polymer; at molecular weights (weight average xe2x80x9cMwxe2x80x9d) of 8000 to 50,000, preference is given to polymer solids contents of 2 wt. % to 25 wt. % polymer, preferably 5 wt. % to 22 wt. % polymer, particularly preferably to polymer solids contents of 7 wt. % to 20 wt. %, and at molecular weights (Mw) greater than 50,000, preference is given to polymer solids contents of 2 wt. % to 15 wt. % polymer.
The molecular weight (weight average Mw) is determined by means of gel permeation chromatography (GPC) with methylene chloride as eluant. Detection is by means of UV or refractive index (RI). Columns based on polystyrene gels, calibrated against polycarbonate, are used. In the present case, a HP 1050 was used.
The organic solvent for the polycarbonate solution to be washed includes solvents which are solvents for the polycarbonate in question and yield a two-phase mixture with water. These include aliphatic, optionally branched, partially halogenated or perhalogenated solvents having from 1 to 10 carbon atoms, with chlorine or fluorine being used as the halogen, such as methylene chloride, trichloroethane, tetrachloroethene, also optionally substituted aromatic compounds having from 6 to 18 carbon atoms, such as benzene, toluene, o-, m- and/or p-xylene, methoxy- or ethoxy-benzene, diphenyl, diphenyl ether, chlorobenzene, o-, m- and/or p-dichlorobenzene, as well as mixtures of such solvents. Preferred solvents are methylene chloride and chlorobenzene, especially chlorobenzene.
Suitable chain terminators are both monophenols and monocarboxylic acids. Suitable monophenols are phenol, alkylphenols such as cresols, p-tert-butylphenol, p-n-octylphenol, p-isooctylphenol, p-n-nonylphenol and p-isononylphenol, halophenols such as p-chlorophenol, 2,4-dichlorophenol, p-bromophenol and 2,4,6-tribromophenol, and mixtures thereof.
Suitable monocarboxylic acids are benzoic acid, alkylbenzoic acids and halobenzoic acids.
The amount of chain terminator to be used is from 0.5 mol % to 10 mol %, based on moles of diphenols used in a particular case. The addition of the chain terminators may take place before, during or after the phosgenation.
Suitable branching agents are the tri- or poly-functional compounds known in polycarbonate chemistry, especially those having three or more phenolic OH groups.
Suitable branching agents are, for example, phloroglucinol, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 2,4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane, 1,3,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane, tri-(4-hydroxyphenyl)-phenylmethane, 2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane, 2,4-bis-(4-hydroxyphenyl-isopropyl)-phenol, 2,6-bis-(2-hydroxy-5xe2x80x2-methyl-benzyl)-4-methylphenol, 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane, hexa-(4-(4-hydroxyphenyl-isopropyl)phenyl)-orthoterephthalic acid ester, tetra-(4-hydroxyphenyl)-methane, tetra-(4-(4-hydroxyphenyl-isopropyl)-phenoxy)-methane and 1,4-bis-(4xe2x80x2,4xe2x80x3-dihydroxy-triphenyl)-methyl)-benzene, as well as 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole or a mixture thereof.
The amount of branching agents that are optionally to be used is 0.05 mol % to 2.5 mol %, preferably 0.1 to 1.0 mol %, based on moles of diphenols used in a particular case.
The branching agents may either be used initially with the diphenols and the chain terminators in the aqueous alkaline phase, or they may be added in solution in an organic solvent before the phosgenation.
All these measures for the preparation of the polycarbonates are known to the person skilled in the art.